It is sometimes desirable to generate a reference signal having a known frequency and phase shift. For example, phase sensitive detectors, also known as lock-in amplifiers, are utilized for extracting a signal having a known carrier. The phase sensitive detector converts the extracted signal's phase and amplitude to a DC voltage signal or a time-varying low-frequency signal. A phase sensitive detector typically requires a reference signal having the same frequency as the carrier to demodulate and extract the signal.